The use of CO2 which can be recovered in value as carbon source for the production of chemical consumables is a key challenge in order to reduce its accumulation in the atmosphere but also in order to control our dependence on fossil fuels.
The greatest challenge faced by scientists and industrialists is to recycle CO2, that is to say, to develop reactions which make it possible to produce chemical compounds, such as, for example, fuels, plastic polymers, medicaments, detergents, high tonnage molecules, conventionally obtained by petrochemical methods. The technical difficulty lies in the development of chemical reactions which make it possible to functionalize the CO2 while reducing the central carbon atom (i.e., by replacing the C—O bonds of the CO2 with C—H or C—C bonds).
In view of the high thermodynamic stability of carbon dioxide, its conversion into novel chemical consumables necessarily involves an external energy source so as to promote the thermodynamic balance of the chemical transformation represented in FIG. 1.
Today, all the efforts of the scientific community are focused on the use of electricity or light to carry out the electroreduction or photoreduction of the CO2 to give formic acid, methanal, methanol and methane (Morris, A. J., Meyer, G. J. and Fujita, E., Accounts Chem. Res., 2009, 42 1983). In fact, this field of research is the subject of intense international competition.
A recent paper describes that the use of silane compounds makes it possible to reduce CO2 under organocatalytic conditions (Riduan, S. N., Zhang, Y. G. and Ying, J. Y., Angewandte Chemie-International Edition, 2009, 48, 3322). In this case, the silane compound is a reactive entity high in energy and the use of the catalyst promotes the kinetic balance. The authors describe the formation of silyl products of formyl (SiOCHO), acetal (SiOCH2OSi) and methoxy (SiOCH3) types. While this strategy is justified by the importance of the uses of the reduction products of CO2 in the chemical industry (HCOOH, H2CO, CH3OH), it should nevertheless be noted that these molecules are currently used on a scale which remains very low with respect to the amount of available CO2 which can be recovered in value. In other words, if these molecules were produced exclusively from CO2, they would make it possible to recover in value, taking into account the current market, only 3.4% of the CO2 produced each year which can be recovered in value (2.5 Gt/year) (Panorama des voies de valorisation du CO2 [Overview of the routes for recovering CO2 in value], ADEME, June 2010, http://www2.ademe.fr/servlet/getDoc?cid=96&m=3&id=72052 &p1=30&ref=12441).
Thus, it is necessary to try to diversify the nature and the number of chemical consumables which can be obtained from CO2.
Another strategy for the conversion of CO2 into novel chemical consumables consists in using a reactive (high in energy) chemical partner to promote the thermodynamic balance of the chemical transformation of CO2. This strategy is also not very well represented on the scientific scene but it will make it possible, in the long run, to considerably open up the supply of molecules available from CO2. The only industrial process based on this approach is the synthesis of urea obtained by condensation of ammonia with CO2, as shown in equation 1 below (Sakakura, T., Choi, J. C. and Yasuda, H., Chem. Rev., 2007, 107, 2365).

According to the same principle, the synthesis of polycarbonates by CO2/epoxides copolymerization is in the process of industrialization as shown in equation 2 below (Panorama des voies de valorisation du CO2 [Overview of the routes for recovering CO2 in value], ADEME, June 2010, http://www2.ademe.fr/servlet/getDoc?cid=96&m=3&id=72052 &p1=30&ref=12441).

In both these syntheses (equations 1 and 2), there is no formal reduction of the central carbon atom of the CO2.
Still with the aim of obtaining novel chemical consumables, it is possible to envisage converting the CO2 into amine compounds and more specifically into methylated amines. Methylated amines (of general formula R1R2NCH3) are a class of chemical compounds which are important in the chemical industry, where they are commonly used as solvents, reactants, fertilizers, herbicides, fungicides, active principles for medicaments and precursors of plastics (Amines: Synthesis, Properties and Applications, Lawrence, S. A., Cambridge University Press, 2006; Arpe, H.-J. and Hawkins, S., Industrial Organic Chemistry, Wiley-VCH, Weinheim, 1997; M. F. Ali; B. M. El Ali and J. G. Speight, Handbook of Industrial Chemistry—Organic Chemicals, McGraw-Hill, New York, 2005).
Methylated amines (of general formula R1R2NCH3) are generally synthesized by reaction between an amine of general formula R1R2NH and an electrophilic methylating agent, such as methyl iodide, methanol, dimethyl sulfate or dimethyl carbonate, preferably in the presence of a base.
Alternatively, methylated amines can be obtained by employing paraformaldehyde in the presence of a reducing agent (H2, NaBH4).
These different synthetic routes thus do not involve CO2 as carbon source for the methylation of the N—H bond of the amine.
The synthesis of methylated amines from CO2 is not very extensively described. It is in particular described by three publications:                In 1985, Ram and Ehrenkaufer described the carboxylation of amines in the presence of CO2. After alkylation or silylation, the carbamic esters obtained are reduced with lithium aluminum hydride (LiAlH4) (S. Ram and R. E. Ehrenkaufer, Tetrahedron Lett., 1985, Vol. 26, Issue 44, pp. 5367-5370).        According to a similar strategy, a three-stage method was developed by Jung et al.: the first stage consists in carrying out the carbonation of the amine in the presence of cesium carbonate. In a second stage, the carbamate thus formed is covalently grafted to a “Merrifield” resin. Finally, the carbamic ester supported on resin is reduced to methylated amine by reduction with lithium aluminum hydride (LiAlH4) (R. N. Savatore, F. X. Chu, A. S. Nagle, E. A. Kapxhiu, R. M. Cross and K. W. Jung, Tetrahedron, 2002, Vol. 58, pp. 3329-3347).        A different strategy was developed by Ram and Spicer in 1989. It is based on the silylation of the N—H bond of an amine by hexamethyldisilazane (Me3SiSiMe3), followed by reaction with CO2 in the presence of lithium aluminum hydride (LiAlH4) (S. Ram and L. D. Spicer, Synthetic Communications, 1989, Vol. 19, pp. 3561-3571).        
These synthetic routes exhibit disadvantages, in particular:                the source of hydrides is LiAlH4, a harsh reducing agent incompatible with the presence of functional groups on the amines;        the processes involve several stages which require intermediate purifications;        the reactions are not catalytic, which compels the use of powerful reactants (such as LiAlH4) and the use of multiple stages for improving the yields and selectivities.        
In the context of the synthesis of methylated amines using carbon dioxide, the technical challenge to be answered is that of combining the functionalization of the carbon dioxide (formation of a C—N bond) with a stage of chemical reduction (formation of three C—H bonds). In order to maximize the energy efficiency of such a transformation, it is necessary to develop reactions with a limited number of stages (ideally just one) and which are catalyzed, in order to prevent energy losses of a kinetic nature.
Labeled methylated amines, incorporating radioactive isotopes and/or stable isotopes, are moreover of particular interest in many fields, such as, for example, in life sciences (study/elucidation of enzymatic mechanisms or of biosynthetic mechanisms, in biochemistry and the like), environmental sciences (tracing of waste, and the like), research (study/elucidation of reaction mechanisms) or the research and development of novel pharmaceutical and therapeutic products. Thus, to develop a synthesis for the preparation of labeled methylated amines meeting the requirements indicated above meets a real need.
There thus exists a real need for a process for preparing methylated amines by the transformation of CO2 which overcomes the disadvantages of the prior art, said process making it possible to combine the functionalization of the carbon dioxide with a stage of chemical reduction.
In particular, there exists a real need for a process which makes it possible to obtain, in just one step and with a good, indeed even excellent, selectivity, methylated amines from CO2 and amines, under catalytic conditions and in the presence of a compound which provides for the reduction of CO2 and which is compatible with the presence of functional groups on the amine.
In addition, there exists a real need to have available a process which makes it possible to obtain, in just one step and with an excellent selectivity, labeled methylated amines incorporating radioactive isotopes and/or stable isotopes starting from labeled reactants, such as, for example, labeled CO2 and/or labeled amines, under catalytic conditions and in the presence of a compound which provides for the reduction of CO2 and which is compatible with the presence of functional groups on the amine.